1. Field of the Invention
The present invention relates to an improved, self-contained exhaust hood for placement above a cooking surface in order to effect the removal of smoke, cooking odors and the like while supplying fresh air to the work area. The unit is designed to achieve optimum removal of fouled air, while requiring only a minimum of make-up air from the tempered room air, thus reducing overall energy consumption.
2. The Prior Art
Many self-contained cooking exhaust systems are known in the art, all having in common the feature of a make-up air duct located within the exhaust hood for supplying make-up air from a source other than the temperature-controlled (tempered) room air. However, all of the arrangements proposed until now have had a number of disadvantages which make their use less than ideal.
For example, U.S. Pat. No. 3,457,850 describes an "air curtain" ventilating hood which is operable in one of two modes. In a first mode, when the outside, or make-up air is at a relatively low temperature a single curtain of make-up air from the outside is passed through the hood from a register at the interior of the lower front hood wall to an exhaust area at the upper rear hood wall. Since the make-up air is not directed beyond the lower lip of the hood the apparatus must rely exclusively upon convective forces to raise the heated, fouled cooking air into the relatively cooler make-up air curtain for entrainment and exhaust. The ventilator hood must not be raised very high above the cooking area or the scavenging function of the make-up air curtain is lost.
The ventilator hood of U.S. Pat. No. 3,457,850 may be operated in a second mode when the make-up air temperature is relatively high. In this second mode, a secondary air curtain is projected outwardly from the front hood wall into the room, the secondary air curtain passing just beneath the lower lip of the front hood wall into the make-up air curtain described above. This second mode of operation results in still further disadvantages. First, a discomfiting draft past the cook's head is realized from the secondary air curtain. Secondly, no significant additional entrainment of the fouled cooking air obtains and, in fact, the first-mentioned make-up air curtain is reduced by the amount of air supplied to the secondary air curtain. Finally, the projection of make-up air to the kitchen results in added heat loading of the restaurant air-conditioning system, which increases the cost of operation markedly.
Another exhaust hood arrangement is taught in U.S. Pat. No. 3,890,887 which comprises a modification of the hood described above with respect to U.S. Pat. No. 3,457,850. In the '887 design a "ventilation door" is installed in the lower front hood wall for downwardly directing a flow of make-up air on or behind the cook in order to maintain temperature control at work stations adjacent to the cooking area located beneath the exhaust hood. Louvers are provided in the register at the lower front hood wall for directing the primary make-up air curtain from this register inwardly of the hood toward the exhaust area at the upper rear hood wall. The modified exhaust hood of U.S. Pat. No. 3,890,887 serves well to cool the kitchen in work areas apart from the cooking area, but suffers the disadvantage of reducing the effectiveness of the exhaust-bound air curtain by the amount of make-up air used to temper the kitchen environment, as well as having the drawbacks of the U.S. Pat. No. 3,457,850 vent hood.
A further exhaust hood for fouled cooking air is taught in U.S. Pat. No. 3,664,255. This device utilizes the make-air flow from lower front to upper rear walls of the hood. However, it relies heavily on convective forces to raise the fouled cooking air into the make-up air stream and does not provide adequate means for lifting the fouled air into entrainment with the hood-contained make-up air stream. Although a supplemental air stream is directed inwardly from the front hood wall lower edge, it does not extend downwardly out of the hood and does not serve to lift the main body of fouled air toward the exhaust vent.